U.S. patent number 7,664,202 [Application Number 11/547,354] was granted by the patent office on 2010-02-16 for transmission device and wireless communication apparatus.
This patent grant is currently assigned to Panasonic Corporation. Invention is credited to Yoshihiro Hara, Toru Matsuura.
United States Patent |
7,664,202 |
Hara , et al. |
February 16, 2010 |
**Please see images for:
( Certificate of Correction ) ** |
Transmission device and wireless communication apparatus
Abstract
In a first mode in which the power level of a transmission
output signal (S6) is to be high, an output from the multiplier (2)
is input to an amplitude modulation signal amplifier (4), and a
radio frequency power amplifier (5) performs amplitude modulation
on a radio frequency phase modulated signal (S4) using a nonlinear
area with a supply voltage from the amplitude modulation signal
amplifier (4). In a second mode in which the power level of a
transmission output signal (S6) is to be low, the output from the
multiplier (2) is input to a variable gain amplifier (7), and the
variable gain amplifier (7) performs amplitude modulation on the
radio frequency phase modulated signal (S4). The amplitude
modulated signal is output without passing through the radio
frequency power amplifier (5).
Inventors: |
Hara; Yoshihiro (Osaka,
JP), Matsuura; Toru (Osaka, JP) |
Assignee: |
Panasonic Corporation (Osaka,
JP)
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Family
ID: |
36777276 |
Appl.
No.: |
11/547,354 |
Filed: |
February 2, 2006 |
PCT
Filed: |
February 02, 2006 |
PCT No.: |
PCT/JP2006/001775 |
371(c)(1),(2),(4) Date: |
September 29, 2006 |
PCT
Pub. No.: |
WO2006/082894 |
PCT
Pub. Date: |
August 10, 2006 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20070211820 A1 |
Sep 13, 2007 |
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Foreign Application Priority Data
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Feb 3, 2005 [JP] |
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2005-027562 |
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Current U.S.
Class: |
375/297;
455/127.2 |
Current CPC
Class: |
H03F
3/24 (20130101); H03F 1/0205 (20130101); H03F
1/02 (20130101); H03F 1/0227 (20130101); H03F
3/72 (20130101); H03F 2200/324 (20130101); H03F
2200/451 (20130101) |
Current International
Class: |
H04L
25/49 (20060101) |
Field of
Search: |
;375/300,302,297
;455/108,110,127.1,127.2,127.5,93,102
;330/51,296,273,127,199,200,259,290 ;323/266 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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1 450 479 |
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Aug 2004 |
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EP |
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1 598 943 |
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Nov 2005 |
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EP |
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2001-156554 |
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Jun 2001 |
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JP |
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3207153 |
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Jul 2001 |
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JP |
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2004-104194 |
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Apr 2004 |
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JP |
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2004-289812 |
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Oct 2004 |
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JP |
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2005-20693 |
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Jan 2005 |
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JP |
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02/084864 |
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Oct 2002 |
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WO |
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Other References
Supplementary European Search Report dated Jun. 10, 2009 for
European Application No. 06 71 2918. cited by other.
|
Primary Examiner: Fan; Chieh M
Assistant Examiner: Fotakis; Aristocratis
Attorney, Agent or Firm: Wenderoth, Lind & Ponack,
L.L.P.
Claims
The invention claimed is:
1. A transmission device using polar modulation, comprising: an
amplitude/phase separation section for separating an input baseband
modulation signal into a baseband amplitude modulation signal and a
baseband phase modulation signal; a frequency synthesizer for
performing phase modulation on a radio frequency carrier signal
with the baseband phase modulation signal to generate a radio
frequency phase modulated signal; a multiplier for multiplying the
baseband amplitude modulation signal by a predetermined value; a
first switching section and a second switching section for allowing
the baseband amplitude modulation signal, obtained as a result of
the multiplication and output from the multiplier, and a
predetermined DC voltage signal to be input thereto, and selecting
and outputting one of the signals; an amplitude modulation signal
amplifier for supplying a supply voltage based on the signal which
is output from the first switching section; a variable gain
amplifier for amplifying the radio frequency phase modulated signal
generated by the frequency synthesizer in accordance with the
signal which is output from the second switching section; a radio
frequency power amplifier for performing power amplification on the
radio frequency phase modulated signal amplified by the variable
gain amplifier, using the supply voltage supplied from the
amplitude modulation signal amplifier; and a third switching
section and a fourth switching section, respectively provided
before and after the radio frequency power amplifier, for selecting
either to output the radio frequency phase modulated signal
amplified by the variable gain amplifier via the radio frequency
power amplifier or to output the radio frequency phase modulated
signal without using the radio frequency power amplifier; wherein
the switching operation of the first through fourth switching
sections is controlled in accordance with a power level of a signal
which is to be output from the fourth switching section.
2. A transmission device according to claim 1, wherein: in a first
mode in which the power level of the signal which is output from
the fourth switching section is to be higher than a first
predetermined value, the first switching section selects the
multiplied baseband amplitude modulation signal, the second
switching section selects the DC voltage signal, and the third and
fourth switching sections select a path for outputting the radio
frequency phase modulated signal via the radio frequency power
amplifier; and in a second mode in which the power level of the
signal which is output from the fourth switching section is to be
lower than a second predetermined value, the first switching
section selects the DC voltage signal, the second switching section
selects the multiplied baseband amplitude modulation signal, and
the third and fourth switching sections select a path for
outputting the radio frequency phase modulated signal without using
the radio frequency power amplifier.
3. A transmission device according to claim 2, wherein: in a third
mode in which the power level of the signal which is output from
the fourth switching section is to be equal to or lower than the
first predetermined value and equal to or higher than the second
predetermined value, the first switching section selects the DC
voltage signal, the second switching section selects the multiplied
baseband amplitude modulation signal, and the third and fourth
switching sections select a path for outputting the radio frequency
phase modulated signal via the radio frequency power amplifier.
4. A transmission device according to claim 2, wherein the variable
gain amplifier comprises: an amplifier for amplifying the radio
frequency phase modulated signal generated by the frequency
synthesizer; and a multiplier for multiplying the radio frequency
phase modulated signal amplified by the amplifier, by the signal
which is output from the second switching section.
5. A transmission device according to claim 3, wherein the variable
gain amplifier comprises: an amplifier for amplifying the radio
frequency phase modulated signal generated by the frequency
synthesizer; and a multiplier for multiplying the radio frequency
phase modulated signal amplified by the amplifier, by the signal
which is output from the second switching section.
6. A transmission device according to claim 1, further comprising:
a phase correction section for storing phase correction
information, for continuously changing a signal phase at a time of
mode switching, for each of a first mode through a third mode; and
an amplitude correction section for storing amplitude correction
information, for continuously changing a signal amplitude at the
time of mode switching, for each of the first through third modes;
wherein: the frequency synthesizer corrects a phase of the radio
frequency phase modulated signal based on the phase correction
information; and the variable gain amplifier corrects an amplitude
of the radio frequency phase modulated signal based on the
amplitude correction information.
7. A transmission device according to claim 1, wherein mode
switching is performed with hysteresis.
8. A transmission device according to claim 1, further comprising
an attenuator inserted on a path, provided by the third and fourth
switching sections, for outputting the radio frequency phase
modulated signal without using the radio frequency power
amplifier.
9. A wireless communication apparatus for transmitting a
transmission signal from an antenna, the wireless communication
apparatus comprising a transmission device according to claim 1,
wherein the transmission signal is processed with power
amplification and is output to the antenna.
10. A wireless communication apparatus for transmitting a
transmission signal from an antenna, the wireless communication
apparatus comprising a transmission device according to claim 2,
wherein the transmission signal is processed with power
amplification and is output to the antenna.
11. A wireless communication apparatus for transmitting a
transmission signal from an antenna, the wireless communication
apparatus comprising a transmission device according to claim 3,
wherein the transmission signal is processed with power
amplification and is output to the antenna.
12. A wireless communication apparatus for transmitting a
transmission signal from an antenna, the wireless communication
apparatus comprising a transmission device according to claim 4,
wherein the transmission signal is processed with power
amplification and is output to the antenna.
13. A wireless communication apparatus for transmitting a
transmission signal from an antenna, the wireless communication
apparatus comprising a transmission device according to claim 5,
wherein the transmission signal is processed with power
amplification and is output to the antenna.
14. A wireless communication apparatus for transmitting a
transmission signal from an antenna, the wireless communication
apparatus comprising a transmission device according to claim 6,
wherein the transmission signal is processed with power
amplification and is output to the antenna.
15. A wireless communication apparatus for transmitting a
transmission signal from an antenna, the wireless communication
apparatus comprising a transmission device according to claim 7,
wherein the transmission signal is processed with power
amplification and is output to the antenna.
16. A wireless communication apparatus for transmitting a
transmission signal from an antenna, the wireless communication
apparatus comprising a transmission device according to claim 8,
wherein the transmission signal is processed with power
amplification and is output to the antenna.
Description
TECHNICAL FIELD
The present invention relates to a transmission device for
amplifying the power of a transmission signal and outputting the
transmission signal, and a wireless communication apparatus using
the same.
BACKGROUND ART
Conventionally, as radio frequency power amplifiers for amplifying
a modulation signal including an envelope fluctuation component,
class A or class AB linear amplifiers have been used in order to
linearly amplify the envelope fluctuation component. Such class A
and class AB linear amplifiers provide a high linearity, but
constantly consume power which accompanies a DC bias component and
so have a lower power efficiency than, for example, class C, D or E
nonlinear amplifiers. This brings about a drawback that when such a
radio frequency power amplifier having a high power consumption is
used in a mobile wireless apparatus having a battery as a power
source, the battery life is short. When such a radio frequency
power amplifier is used for a base station apparatus of a wireless
system including a plurality of high power transmission
apparatuses, the scale of the base station apparatus is enlarged
and the amount of heat generation is increased.
In light of the circumstances, methods for improving the power
efficiency using polar modulation have been conventionally
proposed. FIG. 11 is a block diagram showing a structure of a
conventional transmission device using a polar modulation system.
As shown in FIG. 11, the conventional transmission device includes
an amplitude/phase separation section 61, an amplitude modulation
signal amplifier 62, a frequency synthesizer 63, and a radio
frequency power amplifier 64 as a nonlinear amplifier.
The amplitude/phase separation section 61 separates an input
baseband modulation signal S10 into a baseband amplitude modulation
signal S11 and a baseband phase modulation signal S12. The
amplitude modulation signal amplifier 62 performs predetermined
amplification on the baseband amplitude modulation signal S11, and
then supplies the resultant signal to the radio frequency power
amplifier 64 as a supply voltage. The frequency synthesizer 63
performs phase modulation on a carrier wave signal with the
baseband phase modulation signal S12 to obtain a radio frequency
phase modulated signal S13, and transmits the radio frequency phase
modulated signal S13 to the radio frequency power amplifier 64.
Thus, the radio frequency power amplifier 64 amplifies the radio
frequency phase modulated signal S13 under the supply voltage in
accordance with the baseband amplitude modulation signal S11, and
outputs the resultant signal as a transmission output signal
S14.
Now, an operation of the transmission device using the polar
modulation system will be described. Where the baseband modulation
signal S10 is Si (t), Si (t) is represented by expression (1).
Here, a(t) represents amplitude data, and exp [j.phi.(t)]
represents phase data. Si(t)=a(t)exp[j.phi.(t)] (1)
The amplitude/phase separation section 61 extracts amplitude data
a(t) and phase data exp[j.phi.(t)] from Si(t). The amplitude data
a(t) corresponds to the baseband amplitude modulation signal S11,
and the phase data [j.phi.(t)] corresponds to the baseband phase
modulation signal S12. The amplitude data a(t) is amplified by the
amplitude modulation signal amplifier 62 and is supplied to the
radio frequency power amplifier 64. Thus, the value of the supply
voltage of the radio frequency power amplifier 64 is set based on
the amplitude data a(t).
The frequency synthesizer 63 generates the radio frequency phase
modulated signal S13 by modulating carrier wave angular frequency
.omega.c with the phase data exp[j.phi.(t)], and inputs the radio
frequency phase modulated signal S13 to the radio frequency power
amplifier 64. Where the radio frequency phase modulated signal S13
is signal Sc, signal Sc is represented by expression (2).
Sc=exp[.omega.ct+.phi.(t)] (2)
Since the radio frequency power amplifier 64 is a nonlinear
amplifier, the supply voltage value a(t) of the radio frequency
power amplifier 64 is multiplied by the output signal from the
frequency synthesizer 63, and the resultant signal is amplified by
gain G to generate the transmission output signal S14. The
transmission output signal S14 is output from the radio frequency
power amplifier 64. Where the transmission output signal S14 is RF
signal Srf, RF signal Srf is represented by the expression (3).
Srf=Ga(t)Sc=Ga(t) exp[.omega.ct+.phi.(t)] (3)
The signal which is input to the radio frequency power amplifier 64
is a phase modulated signal which has no fluctuation component in
the amplitude direction and so is a constant envelope signal. This
allows a highly efficient nonlinear amplifier to be used as the
radio frequency power amplifier 64, and therefore a highly
efficient transmission device can be provided. The technologies
using this type of polar modulation system are described in, for
example, patent document 1 and patent document 2.
Patent document 1: Japanese Patent No. 3207153
Patent document 2: Japanese Laid-Open Patent Publication No.
2001-156554
Patent document 3: U.S. Pat. No. 6,191,653
DISCLOSURE OF THE INVENTION
Problems to be Solved by the Invention
The above-described conventional transmission device using the
polar modulation system uses the radio frequency power amplifier 64
as a nonlinear amplifier in an output saturation state in
accordance with the supply voltage. Therefore, an input level to
the radio frequency power amplifier 64 needs to be high to some
extent. However, when the input level is raised, there are problems
that it becomes difficult to obtain a transmission output signal,
especially a signal of a low output level, due to the power leaking
from the input to the output of the radio frequency power amplifier
64, operation limit of the transistor at a low supply voltage and
the like.
Therefore, an object of the present invention is to provide a
transmission device capable of controlling a wide range of
transmission output level from a low output level to a high output
level with a high power efficiency, and a wireless communication
apparatus using such a transmission device.
Solution to the Problems
The present invention is directed to a transmission device using
polar modulation, and a wireless communication apparatus for
transmitting a transmission signal from an antenna. In order to
attain the above-described object, a transmission device according
to the present invention comprises an amplitude/phase separation
section, a frequency synthesizer, a multiplier, first through
fourth switching sections, an amplitude modulation signal
amplifier, a variable gain amplifier, and a radio frequency power
amplifier. A wireless communication apparatus according to the
present invention comprises the above-described transmission
device, wherein a transmission signal is processed with power
amplification and is output to the antenna.
The amplitude/phase separation section separates an input baseband
modulation signal into a baseband amplitude modulation signal and a
baseband phase modulation signal. The frequency synthesizer
performs phase modulation on a radio frequency carrier signal with
the baseband phase modulation signal to generate a radio frequency
phase modulated signal. The multiplier multiplies the baseband
amplitude modulation signal by a predetermined value. The first
switching section and a second switching section allow the baseband
amplitude modulation signal, obtained as a result of the
multiplication and output from the multiplier, and a predetermined
DC voltage signal to be input thereto, and select and output one of
the signals. The amplitude modulation signal amplifier supplies a
supply voltage based on the signal which is output from the first
switching section. The variable gain amplifier amplifies the radio
frequency phase modulated signal generated by the frequency
synthesizer in accordance with the signal which is output from the
second switching section. The radio frequency power amplifier
performs power amplification on the radio frequency phase modulated
signal amplified by the variable gain amplifier, using the supply
voltage supplied from the amplitude modulation signal amplifier.
The third switching section and a fourth switching section,
respectively provided before and after the radio frequency power
amplifier, select either to output the radio frequency phase
modulated signal amplified by the variable gain amplifier via the
radio frequency power amplifier or to output the radio frequency
phase modulated signal without using the radio frequency power
amplifier. Using such a structure, the switching operation of the
first through fourth switching sections is controlled in accordance
with a power level of a signal which is to be output from the
fourth switching section.
Typically, in a first mode in which the power level of the signal
which is output from the fourth switching section is to be higher
than a first predetermined value, the first switching section
selects the multiplied baseband amplitude modulation signal, the
second switching section selects the DC voltage signal, and the
third and fourth switching sections select a path for outputting
the radio frequency phase modulated signal via the radio frequency
power amplifier. In a second mode in which the power level of the
signal which is output from the fourth switching section is to be
lower than a second predetermined value, the first switching
section selects the DC voltage signal, the second switching section
selects the multiplied baseband amplitude modulation signal, and
the third and fourth switching sections select a path for
outputting the radio frequency phase modulated signal without using
the radio frequency power amplifier.
Preferably, in a third mode in which the power level of the signal
which is output from the fourth switching section is to be equal to
or lower than the first predetermined value and equal to or higher
than the second predetermined value, the first switching section
selects the DC voltage signal, the second switching section selects
the multiplied baseband amplitude modulation signal, and the third
and fourth switching sections select a path for outputting the
radio frequency phase modulated signal via the radio frequency
power amplifier.
The above-described variable gain amplifier may comprise an
amplifier for amplifying the radio frequency phase modulated signal
generated by the frequency synthesizer; and a multiplier for
multiplying the radio frequency phase modulated signal amplified by
the amplifier, by the signal which is output from the second
switching section.
The transmission device may further comprise a phase correction
section and an amplitude correction section for storing, for each
of the first through third modes, phase correction information and
amplitude correction information, for continuously changing a
signal phase and a signal amplitude at the time of mode switching.
In this case, the frequency synthesizer may correct the phase of
the radio frequency phase modulated signal based on the phase
correction information; and the variable gain amplifier may correct
the amplitude of the radio frequency phase modulated signal based
on the amplitude correction information.
The mode switching may be performed with hysteresis.
An attenuator may be inserted on a path, provided by the third and
fourth switching sections, for outputting the radio frequency phase
modulated signal without using the radio frequency power
amplifier.
Effect of the Invention
A transmission device according to the present invention selects
the optimum operation mode from a plurality of operation modes in
accordance with the output power level of the radio frequency power
amplifier, and optimally controls the leak from the input to the
output of the radio frequency power amplifier. Thus, the power
amplification can be performed with a high power efficiency and a
high linearity, and the transmission output power can be controlled
in a wide range from a high level to a low level. In addition, the
discontinuous change in the amplitude and the phase of the output
signal which accompanies the switching of the operation mode is
prevented, and thus the amplitude and the phase are changed
continuously. Therefore, problems including transitional spectrum
expansion accompanying the switching can be suppressed.
BRIEF DESCRIPTION OF THE DRAWINGS
[FIG. 1] FIG. 1 is a block diagram showing a schematic structure of
a transmission device according to a first embodiment of the
present invention.
[FIG. 2] FIG. 2 shows operation modes switchable by the
transmission device according to the present invention.
[FIG. 3] FIG. 3 illustrates a circuit configuration of a radio
frequency power amplifier 5 used as a nonlinear amplifier.
[FIG. 4] FIG. 4 illustrates an operation of the radio frequency
power amplifier 5 used as a nonlinear amplifier.
[FIG. 5] FIG. 5 is a block diagram showing a schematic structure of
a transmission device according to a second embodiment of the
present invention.
[FIG. 6] FIG. 6 is a flowchart illustrating a method by which the
transmission device according to the second embodiment switches the
operation mode in FIG. 2.
[FIG. 7] FIG. 7 shows a hysteresis characteristic when the
transmission device according to the second embodiment switches the
operation mode in FIG. 2.
[FIG. 8A] FIG. 8A illustrates a continuous change in the amplitude
of the transmission output signal by the transmission device
according to the present invention.
[FIG. 8B] FIG. 8B illustrates a continuous change in the phase of
the transmission output signal by the transmission device according
to the present invention.
[FIG. 9A] FIG. 9A is a block diagram showing another schematic
structure based on the transmission device according to the second
embodiment of the present invention.
[FIG. 9B] FIG. 9B is a block diagram showing still another
schematic structure based on the transmission device according to
the second embodiment of the present invention.
[FIG. 10] FIG. 10 is a block diagram showing a wireless
communication apparatus including the transmission device according
to the present invention.
[FIG. 11] FIG. 11 is a block diagram showing a schematic structure
of a conventional transmission device.
DESCRIPTION OF THE REFERENCE CHARACTERS
1, 61 Amplitude/phase separation section
2, 17 Multiplier
3, 8, 9, 14 Switching section
4, 62 Amplitude modulation signal amplifier
5, 64 Radio frequency power amplifier
6, 63 Frequency synthesizer
7 Variable gain amplifier
11 Phase correction section
12 Amplitude correction section
15 Control section
16 Amplifier
20 Wireless communication apparatus
21 Transmission device
22 Receiving device
23 Transmission/receiving switching section
24 Antenna
50 Nonlinear amplifier
51 Parasitic capacitance
BEST MODE FOR CARRYING OUT THE INVENTION
First Embodiment
FIG. 1 is a block diagram showing a schematic structure of a
transmission device using a polar modulation system according to a
first embodiment of the present invention. As shown in FIG. 1, the
transmission device according to the first embodiment includes an
amplitude/phase separation section 1, a multiplier 2, an amplitude
modulation signal amplifier 4, a radio frequency power amplifier 5,
a frequency synthesizer 6, a variable gain amplifier 7, a control
section 15, and first through fourth switching sections 3, 8, 9 and
14.
The amplitude/phase separation section 1 separates an input
baseband modulation signal S1 into a baseband amplitude modulation
signal S2 and a baseband phase modulation signal S3. The multiplier
2 multiplies the baseband amplitude modulation signal S2 by an
average output level specifying signal SL supplied from the control
section 15. The first switching section 3 selects either an output
signal from the multiplier 2 or an DC voltage signal SV from the
control section 15 based on a mode switching signal SM given from
the control section 15, and outputs the selected signal to the
amplitude modulation signal amplifier 4. The amplitude modulation
signal amplifier 4 supplies a supply voltage, in accordance with
the signal selected by the first switching section 3, to the radio
frequency power amplifier 5. The frequency synthesizer 6 performs
phase modulation on a carrier wave signal with the baseband phase
modulation signal S3 to generate a radio frequency phase modulated
signal S4. The second switching section 8 selects either the output
signal from the multiplier 2 or the DC voltage signal SV from the
control section 15 based on the mode switching signal SM, and
outputs the selected signal to the variable gain amplifier 7 as a
gain control signal S5. The variable gain amplifier 7 controls the
gain of the radio frequency phase modulated signal S4 generated by
the frequency synthesizer 6, in accordance with the gain control
signal S5 which is output from the second switching section 8. The
radio frequency power amplifier 5 amplifier the power of a signal
which is input from the variable gain amplifier 7 in accordance
with the supply voltage given from the amplitude modulation signal
amplifier 4, and outputs the obtained signal as a transmission
output signal S6. The third and fourth switching sections 9 and 14
select, based on the mode switching signal SM, either to input the
output signal from the variable gain amplifier 7 to the radio
frequency power amplifier 5 or to let the signal pass to be output
without inputting the signal to the radio frequency power amplifier
5. The fourth switching section 14 may be of any form as long as
having a switching function. For example, the fourth switching
section 14 may be an FET switch, a diode switch, or a transmission
path having a high impedance as seen from the branching point.
The control section 15 determines the operation mode of the radio
frequency power amplifier 5 and controls the connection states such
that the transmission device has a circuit corresponding to the
determined operation mode. The operation mode is determined by a
transmission power level, which is based on a receiving signal
state specified by the wireless base station or a receiving signal
state in the transmission device, and by the characteristics of the
radio frequency power amplifier 5. Typically, from the viewpoint of
the power efficiency, when the power level of the transmission
output signal S6 is to be high, an operation mode in which the
radio frequency power amplifier 5 operates as a nonlinear amplifier
is desirable. When the power level of the transmission output
signal S6 is to be low (outside the range in which the radio
frequency power amplifier 5 is operable as a nonlinear amplifier),
an operation mode in which the radio frequency power amplifier 5
operates as a linear amplifier is desirable. A signal for switching
the operation mode is the mode switching signal SM. For example, a
2-bit mode switching signal may be used to output "01" when the
transmission power level is to be high and to output "10" when the
transmission power level is to be low. The average output level
specifying signal SL is for specifying an average power level of
the signals which are output from the transmission device. The DC
voltage signal SV is a fixed voltage for controlling the gain of
the amplitude modulation signal amplifier 4 and the variable gain
amplifier 7. The control section 15 may be provided either in the
transmission device or outside the transmission device.
Hereinafter, an operation of the transmission device having the
above-described structure according to the first embodiment will be
described. In the following example, the transmission device is
operable in three operation modes: an operation mode in which the
power level of the transmission output signal S6 is to be high
(first mode), medium (third mode), and low (second mode) (see FIG.
2).
(1) First Mode
When the power level of the transmission output signal S6 is high,
the first mode is selected by the control section 15 in order to
allow the radio frequency power amplifier 5 to operate as a
nonlinear amplifier in a saturation operation range or a switching
operation range. In the first mode, the first and second switching
sections 3 and 8 each select "terminal b", and the third and fourth
switching sections 9 and 14 each select "terminal a". To the
multiplier 2, an average output level specifying signal SL in
accordance with the first mode is output.
The baseband amplitude modulation signal S2 separated by the
amplitude/phase separation section 1 is multiplied by the average
output level specifying signal SL by the multiplier 2. The
resultant multiplication product signal is output to the amplitude
modulation signal amplifier 4 via the first switching section 3.
The amplitude modulation signal amplifier 4 amplifies the input
multiplication product signal and outputs the resultant signal to
the radio frequency power amplifier 5 as a supply voltage. The
radio frequency power amplifier 5 uses the supply voltage to
perform amplitude modulation on the input phase modulated signal
S4. In order to generate the supply voltage to be given to the
radio frequency power amplifier 5 in accordance with the level of
the baseband amplitude modulation signal S2 at a high efficiency,
it is desirable to use a class D amplifier, which represents
amplitude information with a pulse width, as the amplitude
modulation signal amplifier 4.
Meanwhile, the baseband phase modulation signal S3 separated by the
amplitude/phase separation section 1 is used for performing phase
modulation on the carrier wave signal by the frequency synthesizer
6. The radio frequency phase modulated signal S4 generated by the
phase modulation is output to the variable gain amplifier 7. The
variable gain amplifier 7 amplifies (or attenuates) the radio
frequency phase modulated signal S4 based on the gain control
signal S5. The gain control signal S5 is a fixed DC voltage signal
SV supplied via the second switching section 8. Therefore, the
signal which is output from the variable gain amplifier 7 is a
constant envelope signal, which is a phase modulated signal with no
fluctuation component in the amplitude direction. The constant
envelope signal passes through the third switching section 9 and is
processed with amplitude modulation by the radio frequency power
amplifier 5 under the supply voltage. Then, the resultant signal
passes through the fourth switching section 14 and is output as the
transmission output signal S6.
FIG. 3 and FIG. 4 respectively illustrate a circuit configuration
and an operation of the radio frequency power amplifier 5 used as a
nonlinear amplifier. As shown in FIG. 3, the radio frequency power
amplifier 5 can be considered as a nonlinear amplifier 50 having a
parasitic capacitance 51 connected between the input and output. It
is understood that in the nonlinear amplifier 50, where the supply
voltage exceeds a predetermined value, the square of the supply
voltage is in proportion to the output power (the horizontal axis
is a logarithmic axis). It is understood from FIG. 3 and FIG. 4
that the magnitude of the leak current is defined by the level of a
parasitic capacitance 51 and the level of an input signal to the
nonlinear amplifier 50 (the level of the output signal from the
variable gain amplifier 7).
Without the variable gain amplifier 7, the following occurs. The
output from the frequency synthesizer 6 is generally constant and
so the magnitude of the leak power is also constant. Thus, the
level of the transmission output signal S6 can be reduced by
reducing the value of the supply voltage of the nonlinear amplifier
50. However, the value of the supply voltage of the nonlinear
amplifier 50 cannot be reduced to less than a predetermined value
by the restriction by the leak power.
By contrast, in the first embodiment, the gain of the variable gain
amplifier 7 is controlled by the gain control signal S5, and thus
the level of the phase modulated signal S4 which is input to the
radio frequency power amplifier 5 is controlled. This makes it
possible to reduce the leak power. As a result, the range in which
the output power is controlled by the supply voltage (dynamic
range) in the radio frequency power amplifier 5 can be
broadened.
(2) Second Mode
When the power level of the transmission output signal S6 is to be
low, the second mode is selected by the control section 15 in order
to allow the radio frequency power amplifier 5 to operate as a
linear amplifier in a non-saturation operation range. In the second
mode, the first and second switching sections 3 and 8 each select
"terminal a", and the third and fourth switching sections 9 and 14
each select "terminal b". To the multiplier 2, an average output
level specifying signal SL in accordance with the second mode is
output.
The baseband phase modulation signal S3 separated by the
amplitude/phase separation section 1 is used for performing phase
modulation on the carrier wave signal by the frequency synthesizer
6. The radio frequency phase modulated signal S4 generated by the
phase modulation is output to the variable gain amplifier 7. The
baseband amplitude modulation signal S2 separated by the
amplitude/phase separation section 1 is multiplied by the average
output level specifying signal SL by the multiplier 2. The
resultant multiplication product signal, i.e., a signal having an
envelope component (amplitude signal) in proportion to a
multiplication product value of the baseband amplitude modulation
signal S2 and the average output level specifying signal SL, passes
through the second switching section 8 and is output to the
variable gain amplifier 7 as the gain control signal S5. The
variable gain amplifier 7 performs amplitude modulation on the
radio frequency phase modulated signal S4 based on the gain control
signal S5. The signal processed with the amplitude modulation by
the variable gain amplifier 7 passes through the third and fourth
switching sections 9 and 14 and is output as the transmission
output signal S6 without passing through the radio frequency power
amplifier 5.
In the second mode, the radio frequency power amplifier 5 does not
perform amplification. Thus, no power is supplied from the
amplitude modulation signal amplifier 4 to the radio frequency
power amplifier 5, so that the power consumption is suppressed. As
a result, the transmission output signal S6, especially the one
having a low power level, can be output while the power consumption
is significantly reduced. A transmission device having a wide
output power control range down to a low level can be provided. The
power consumption can be suppressed by, for example, giving a 0 V
DC voltage signal SV to the amplitude modulation signal amplifier 4
via the first switching section 3, or by making the amplitude
modulation signal amplifier 4 and the radio frequency power
amplifier 5 non-conductive to each other by a fifth switching
section (not shown) provided therebetween.
(3) Third Mode
When the power level of the transmission output signal S6 is to
have a medium level, the third mode is selected by the control
section 15. In the third mode, the first through fourth switching
sections 3, 8, 9 and 14 each select "terminal a". To the multiplier
2, an average output level specifying signal SL in accordance with
the third mode is output. In the third mode, the radio frequency
power amplifier 5 operates as a linear amplifier in which the input
and the output have a linear relationship.
The baseband amplitude modulation signal S2 separated by the
amplitude/phase separation section 1 is multiplied by the average
output level specifying signal SL by the multiplier 2. The
resultant multiplication product signal passes through the second
switching section 8 and is output to the variable gain amplifier 7
as the gain control signal S5. The amplitude modulation signal
amplifier 4 receives a DC voltage signal SV which is input thereto
via the first switching section 3, and outputs a constant supply
voltage to the radio frequency power amplifier 5.
Meanwhile, the baseband phase modulation signal S3 separated by the
amplitude/phase separation section 1 is used for performing phase
modulation on the carrier wave signal by the frequency synthesizer
6. The radio frequency phase modulated signal S4 generated by the
phase modulation is output to the variable gain amplifier 7. The
variable gain amplifier 7 performs amplitude modulation on the
radio frequency phase modulated signal S4 based on the gain control
signal S5.
When the power level of the transmission output signal S6 is to
have a medium level, the operation of the radio frequency power
amplifier 5 may go outside the nonlinear operation range. Namely,
the linearity of the output power with respect to a change in the
supply voltage may be deteriorated. Even in such a case, in the
third mode, the linearity of the output signal with respect to the
input signal can be maintained and the control range on the output
power level can be broadened, because the radio frequency power
amplifier 5 is operated as a linear amplifier in the third
mode.
As described above, the transmission device according to the first
embodiment of the present invention selects the optimum operation
mode from a plurality of operation modes in accordance with the
output power level of the radio frequency power amplifier 5, and
optimally controls the leak from the input to the output of the
radio frequency power amplifier 5. Thus, the power amplification
can be performed with a high power efficiency and a high linearity,
and the transmission output power can be controlled in a wider
range from a high level to a low level.
In the first embodiment, in the first mode, the gain control signal
S5 supplied to the variable gain amplifier 7 is a fixed DC voltage
signal SV. Alternatively, the gain control signal S5 may be varied
in accordance with the amplitude modulation signal as in the second
and third modes by allowing the radio frequency power amplifier 5
to operate as a nonlinear amplifier, so that the input to the radio
frequency power amplifier 5 is varied in accordance with the
instantaneous output power. In this case also, the same effect is
provided.
In the case where the variable gain amplifier 7 is of a type which
nonlinearly varies in accordance with the gain control signal S5
(for example, having an exponential input/output characteristic),
an element (not shown) having a function of correcting the
nonlinear characteristic into a linear characteristic is inserted
before or after the variable gain amplifier 7.
Alternatively, an attenuator may be inserted into a transmission
path in which the third and fourth switching sections 9 and 14
select terminal b as in the case of the second mode for a low
output power level. Owing to the structure with the attenuator, the
level of the transmission output signal can be further attenuated
and an output signal having a very low level can be transmitted.
Thus, the transmission power can be controlled in a still wider
range.
An amplifier equivalent to the amplitude modulation signal
amplifier 4 may be inserted between an output terminal c of the
second switching section 8 and the variable gain amplifier 7, i.e.,
on a path in which the gain control signal S5 flows.
The delay difference between the amplitude path and the phase path
is different in the first mode (in which the radio frequency power
amplifier 5 performs amplitude modulation) from the second and
third modes (in which the variable gain amplifier 7 performs
amplitude modulation). A functional block for correcting the delay
difference is appropriately added when necessary (not shown).
Second Embodiment
Among the above-described three operation modes, the path of the
radio frequency transmission signal is different. Therefore, the
gain and the phase characteristic of the path is also different
among the three operation modes. For this reason, the amplitude and
the phase of the transmission output signal drastically change when
the operation mode is switched. For example, when the third mode is
switched to the second mode, the following occurs. In the third
mode, the radio frequency transmission signal passes the radio
frequency power amplifier 5; whereas in the second mode, the radio
frequency transmission signal does not pass the radio frequency
power amplifier 5 (passes through the transmission path from the
terminal b of the third switching section 9 to the terminal b of
the fourth switching section 14). Because of the characteristic
difference between the two paths, the amplitude and the phase of
the transmission output signal drastically change.
In a second embodiment, the amplitude and the phase of the
transmission output signal are corrected such that the drastic
change of the signal does not occur (such that the continuity of
the signal is guaranteed) when the operation mode is switched. The
amplitude and the phase of the transmission output signal are
corrected also such that the continuity of the reference phase and
the ACLR characteristic fulfill the standards of the 3GPP (3rd
Generation Partnership Project). The correction on the amplitude
and the phase of the transmission output signal described in the
second embodiment is performed in parallel to the well-known
distortion compensation (see patent document 3) which is
indispensable to the polar modulation system.
FIG. 5 is a block diagram showing a schematic structure of a
transmission device using a polar modulation system according to
the second embodiment of the present invention. As shown in FIG. 5,
the transmission device according to the second embodiment includes
an amplitude/phase separation section 1, a multiplier 2, an
amplitude modulation signal amplifier 4, a radio frequency power
amplifier 5, a frequency synthesizer 6, a variable gain amplifier
7, a phase correction section 11, an amplitude correction section
12, a control section 15, and first through fourth switching
sections 3, 8, 9 and 14. As shown in FIG. 5, the transmission
device according to the second embodiment includes the phase
correction section 11 and the amplitude correction section 12 in
addition to the elements of the transmission device according to
the first embodiment.
Hereinafter, the transmission device according to the second
embodiment will be described mainly regarding the phase correction
section 11 and the amplitude correction section 12.
The phase correction section 11 stores phase correction information
for correcting the phase of the baseband phase modulation signal S3
by the frequency synthesizer 6, in correspondence with each
operation mode. The amplitude correction section 12 stores
amplitude correction information for correcting the amplitude of
the radio frequency phase modulated signal S4 by the variable gain
amplifier 7, in correspondence with each operation mode. The phase
correction information and the amplitude correction information may
be stored in a table form.
FIG. 6 is a flowchart illustrating a method by which the
transmission device according to the second embodiment switches the
operation mode among the three modes (FIG. 2) described in the
first embodiment.
When the polar modulation transmission processing is started, the
average output level specifying signal SL is input to the control
section 15 (step S11). Next, the control section 15 checks the
average output level specifying signal SL to determine whether or
not the operation mode needs to be switched (step S12). The
switching point of the operation mode is not determined only by the
value of the average output level, but by whether the average
output level is increased or decreased. Namely, the switching point
of the operation mode has hysteresis.
FIG. 7 illustrates the hysteresis characteristic during the
operation mode is transferred from the second mode to the third
mode and to the first mode. When the average output level is
changed from a low output level to a medium output level, the
operation mode is transferred from the second mode to the third
mode at point B in FIG. 7. By contrast, when the average output
level is changed from a medium output level to a low output level,
the operation mode is transferred from the third mode to the second
mode at point A in FIG. 7. By providing such a hysteresis
characteristic, even when the average output level is frequently
changed around the switching point of the operation mode, the
number of times that the operation mode is switched can be
minimized so that the continuity of the amplitude and the phase can
be realized with a higher certainty. This is also true when the
operation mode is transferred from the third mode to the first mode
(point D and point E).
When it is determined in step S12 that the operation mode needs to
be switched, the control section 15 outputs a mode switching signal
SM to the phase correction section 11 and the amplitude correction
section 12. The phase correction section 11 selects the phase
correction information corresponding to the mode switching signal
SM, and outputs the selected phase correction information to the
frequency synthesizer 6 (step S13). The amplitude correction
section 12 selects the amplitude correction information
corresponding to the mode switching signal SM, and outputs the
selected amplitude correction information to the variable gain
amplifier 7 (step S13). The frequency synthesizer 6 and the
variable gain amplifier 7 use such correction information to
execute a processing operation.
Owing to the processing operation using the correction information,
the amplitude and the phase can be continuously changed without
being drastically changed between before and after the switching of
the operation mode. FIG. 8A and FIG. 8B respectively illustrate a
continuous change of the amplitude and the phase of the
transmission output signal, which is realized by the transmission
device according to the present invention.
When the mode switching processing in step S13 is completed, or
when it is determined in step S12 that the operation mode does not
need to be switched, it is determined whether or not to terminate
the transmission (step S14). When the transmission is not to be
terminated, the processing returns to step S11 at the start of the
next signal transmission and the loop of steps S12 through S14 is
repeated.
As described above, the transmission device according to the second
embodiment of the present invention selects the optimum operation
mode from a plurality of operation modes in accordance with the
output power level of the radio frequency power amplifier 5, and
optimally controls the leak from the input to the output of the
radio frequency power amplifier 5. Thus, the power amplification
can be performed with a high power efficiency and a high linearity,
and the transmission output power can be controlled in a wide range
from a high level to a low level. In addition, the discontinuous
change in the amplitude and the phase of the output signal which
accompanies the switching of the operation mode is prevented, and
thus the amplitude and the phase are changed continuously.
Therefore, problems including transitional spectrum expansion
accompanying the switching can be suppressed.
In the second embodiment, the phase correction section 11 and the
amplitude correction section 12 respectively output the phase
correction information and the amplitude correction information to
the frequency synthesizer 6 and the variable gain amplifier 7. In
the case where the control section 15 has the phase correction
information and the amplitude correction information, the control
section 15 may directly control the frequency synthesizer 6 and the
variable gain amplifier 7. Alternatively, the transmission output
signal S6 from the radio frequency power amplifier 5 may be
detected, and the detection result may be fed back to the control
section 15. In this case, the continuity of the amplitude and the
phase of the transmission output signal Sb can be realized more
accurately.
As shown in FIG. 9A, the variable gain amplifier 7 described in the
second embodiment may be provided as an amplifier 16 and a
multiplier 17. In this case, the gain control signal S5 which is
output from the second switching section 8 is input to the
multiplier 17. As shown in FIG. 9B, the baseband amplitude
modulation signal S2 may be directly input to the terminal a of the
second switching section 8, instead of the multiplication product
of the baseband amplitude modulation signal S2 and the average
output level specifying signal SL. In this structure, in the second
mode and the third mode, the amplifier 16 controls the average
output level based on the amplitude correction information, and the
multiplier 17 performs amplitude modulation. By allowing the
multiplier 17 to perform amplitude modulation, the envelope of the
output signal can be linearly changed with respect to the amplitude
signal.
The average output level can be controlled in various manners as
described below. For example, in the case where the average output
level is controlled by the output from the second switching section
8, the multiplication product of the average output level
specifying signal SL and the baseband amplitude modulation signal
S2 may be input to the multiplier 17 as an input signal S5. In the
case where the average output level is controlled on a stage after
the multiplier 17, an additional variable gain amplifier may be
provided. In the case where the radio frequency power amplifier 5
performs amplitude modulation, the terminal b of the second
switching section 8 may be selected, so that the DC voltage signal
SV applied to the terminal b is output to the multiplier 17.
In the first and second embodiments, the transmission device
includes the multiplier 2. The multiplier 2 may be omitted as long
as the baseband amplitude modulation signal S2 processed with
average output level control based on the average output level
specifying signal SL is output from the amplitude/phase separation
section 1.
Embodiment of a Wireles Communication Apparatus Including the
Transmission Device According to the Present Invention
FIG. 10 is a block diagram showing a schematic structure of a
wireless communication apparatus 20 including a transmission device
according to the first or the second embodiment described above. As
shown in FIG. 10, the wireless communication apparatus 20 includes
a transmission device 21 and a receiving device 22. The
transmission device 21 and the receiving device 22 are connected to
an antenna 24 via a transmission/receiving switching section 23. As
the transmission device 21, the transmission device according to
the first or the second embodiment is used. The wireless
communication apparatus 20 is, for example, a mobile wireless
communication terminal such as a mobile phone, a mobile information
terminal having a dialog function or the like, or a wireless base
station.
With the wireless communication apparatus 20, at the time of
transmission, the transmission device 21 releases the transmission
output signal S6 from the antenna 24 via the transmission/receiving
switching section 23. At the time of receiving, the receiving
device 22 receives an input receiving signal from the antenna 24
via the transmission/receiving switching section 23 and demodulates
the input receiving signal. When the output power level is to be
high, the radio frequency power amplifier in the transmission
device 21 operates as a nonlinear amplifier, which improves the
power efficiency. With a mobile wireless terminal apparatus or the
like, the battery consumption rate is lowered and thus the battery
life can be extended. The radio frequency power amplifier can be
reduced in size and also can reduce the amount of heat generation,
by the improvement in the power efficiency. This allows a wireless
communication apparatus including this radio frequency power
amplifier to be reduced in size. When the output power level is to
be low, the radio frequency power amplifier can be used as a linear
amplifier, or the signal is allowed to pass through a transmission
path or an attenuator without using the radio frequency power
amplifier. In this way, the output level range can be broadened to
encompass a lower level.
A transmission device according to the present invention, when
applied to a base station apparatus of a wireless system including
a plurality of high power transmission apparatuses, improves the
power efficiency when the output power level is to be high. This
can reduce the size of the radio frequency power amplifier, the
amount of heat generation, and the size of various types of
equipment, and can improve the space efficiency.
INDUSTRIAL APPLICABILITY
The present invention is applicable to a mobile terminal apparatus
such as, for example, a mobile phone or a mobile information
terminal and to a wireless communication apparatus such as, for
example, a wireless base station; and is especially useful for, for
example, controlling the transmission output power over a wide
range with a high power efficiency.
* * * * *